With the development of very large scale integrated (VLSI) circuits, the integration density of semiconductor devices may increase and design rules may decrease. As a result, the distance between adjacent conductive layers at the same level may decrease, which can increase aspect ratios in gaps between conductive layers.
Various technologies for filling a high aspect ratio gap between conductive layers with an insulating material have been developed. Boro-phospho-silicate glass (BPSG) and high density plasma (HDP) oxide are insulating materials that have generally good gap filling properties. Because the formation of BPSG layers typically involves the performance of a reflow process at a temperature of approximately 800° C. or higher, it generally is not used in products having a design rule of 0.15 μm or less due to short channel effects of transistors. Furthermore, because HDP oxide is generally less effective in filling gaps, it typically is not used in products having a design rule of 0.1 μm or less.
To overcome the above problems, spin on glass (SOG) may be used as a gap filling material. Because SOG is deposited in a liquid state, it may be used to fill high aspect ratio gaps between conductive layers in an effective manner. Also, because SOG has a relatively low dielectric constant and may reduce conductive coupling between adjacent conductive layers, it may be used to further increase the integration density of semiconductor devices.
While SOG liquids have generally good gap filling abilities, they are routinely densified through a curing process. During curing, a SOG layer may not be sufficiently cured at points near other layers. During a subsequent wet cleaning process, an SOG layer that is not sufficiently cured may deform due to water absorption from the cleaning solution. Furthermore, the portion of the SOG layer that is not sufficiently cured may be more readily removed due to a relatively high etch rate, which may result in profile defects. For example, in a worst case scenario, an entire SOG layer may be removed, thereby eliminating an interlayer dielectric film. Also, during subsequent thermal processing, outgassing may occur, thereby removing water from the SOG layer. This may cause, for example, via poisoning stemming from oxidation of an exposed metal wiring layer. Even if a SOG layer is successfully cured, because the etch rate of the SOG layer may be relatively high compared to other oxide layers, more serious problems may occur as a design rule decreases.